Our understanding of the role of lipid molecules in cell signaling has grown rapidly in recent years. Yet, we still do not have an understanding of the role of specific fatty acid constituents in affecting the signaling activities of lipids. Work in our laboratory has found that an unusual class of fatty acids, monomethyl branched-chain fatty acids (mmBCFAs), is essential for growth and development of the model organism C. elegans. C. elegans synthesize mmBCFAs de novo and in the absence of this biosynthetic pathway developmental arrest occurs. The experiments described in this proposal are aimed at understanding the essential roles of mmBCFAs in C. elegans growth and development by identifying gene products required to sense inadequate mmBCFA levels, investigating the genetic interactions of mmBCFAs with the daf-2/insulinlike receptor pathway and determining the activity of mmBCFAs on the CeTOR kinase pathway. It is hoped that these studies will enhance our understanding of why certain cells contain particular classes of fatty acids and how specific fatty acids may be modulating lipid signaling pathways.